/* The C language comes with a regular expression engine as standard and
a header file in regex.h. In this example program, we ask the user to
enter a regular expression and then match it against a series of further
strings.

There is a shorter example at reg.c ... this example (reg2.c) caputures
the start and end point of each match and then prints out the string that
matches that part of the incoming string- "capture parenthises" */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <regex.h>

#define MAXMATCH 20

int main () {

        char reginald[81]; /* Regular Expresion */
        char millie[81]; /* Strings to match against */
        char tommy[81]; /* String to hold matched elememts */
        regex_t emma;

        regmatch_t matches[MAXMATCH]; /* Array of matches */
        int status;
        int i;
        int numchars;

        /* Read in and compile a regular expression */

        printf("Please give test expression: ");
        fgets(reginald,80,stdin);
        reginald[strlen(reginald)-1] = '\0';

        /* Let's use extended regular expresssions */

        status = regcomp(&emma,reginald,REG_EXTENDED);
        printf("Validity of regex (0 => OK): %d\n",status);

        /* Leave program if regex is faulty */
        /* we could use regerror to decode the error ... */
        if (status) return 1;

        while (1) {

                /* Loop until an empty line id given */

                printf("Please give test string: ");
                fgets(millie,80,stdin);
                millie[strlen(millie)-1] = '\0';
                if (strlen(millie) < 1) break;

                status = regexec(&emma,millie,MAXMATCH,matches,0);
                printf("Matched (0 => Yes): %d\n",status);
                if (status == 0) {
                        for (i=0; i<MAXMATCH; i++) {
                                if ((int)matches[i].rm_so < 0) break;
                                numchars = (int)matches[i].rm_eo - (int)matches[i].rm_so;
                                strncpy(tommy,millie+matches[i].rm_so,numchars);
                                tommy[numchars] = '\0';
                                printf("From %d to %d (%s)\n",(int)matches[i].rm_so,
                                        (int)matches[i].rm_eo,tommy);
                                }
                        }

                }

        /* Free up memory held within the regex memory */
        regfree(&emma);

        return 0;

        }

/* Sample output:

wizzard:c graham$ ./reg2
Please give test expression: [A-Z]{1,2}[0-9][0-9A-Z]? +[0-9][A-Z]{2}
Validity of regex (0 => OK): 0
Please give test string: We are at SN12 7NY for this course
Matched (0 => Yes): 0
From 10 to 18 (SN12 7NY)
Please give test string:
wizzard:c graham$

wizzard:c graham$ ./reg2
Please give test expression: ([A-Z]{1,2})[0-9][0-9A-Z]? +[0-9][A-Z]{2}
Validity of regex (0 => OK): 0
Please give test string: We are in Birmingham
Matched (0 => Yes): 1
Please give test string: We are at B12 7HJ
Matched (0 => Yes): 0
From 10 to 17 (B12 7HJ)
From 10 to 11 (B)
Please give test string:
wizzard:c graham$

*/